Photoelectrophoretic imaging process employing an insulating carrier liquid containing an unsaturated compound

ABSTRACT

THIS INVENTION RELATES TO A MONOCHROMATIC IMAGING SYSTEM UTILIZING AN IMAGING SUSPENSION COMPRISING A PHOTORESPONSIVE PIGMENT DISPERSED IN AN INSULATING CARRIER LIQUID. THE INSULATING LIQUID CARRIER UTILIZED IN THE PROCESS COMPRISES A SUBSTANTIALLY NON-VOLATILE, UNSATURTED ORGANIC COMPOSITION WHICH IS IN LIQUID FORM AT ROOM TEMPERATURE. THE SUSPENSION IS INTERPOSITIONED BETWEEN A PAIR OF ELEC-   TRODES AND SUBJECTED TO A POTENTIAL DIFFERENCE WHILE SIMULTANEOUSLY BEING SELECTIVELY EXPOSED TO A LIGHT IMAGE. THE MONOCHROMATIC IMAGING PROCESS OF THE PRESENT INVENTION PRODUCES RELATIVELY HIGH CONTRAST, BACKGROUND FREE IMAGES IN A SINGLE PASS SYSTEM.

Sept. 19, 1972 R. L. JELFO 3,692,517

PHOTOELECTROPHORETIC IMAGING PROCESS EMPLOYING AN INSULATING CARRIER LIQUID CONTAINING AN UNSATURATED COMPOUND Filed May 29, 1967 INVENTOR. RAYMOND L. JELFO BY fiwuw ATTORNEYS United States Patent Oifice 3,692,517 PHOTOELECTROPHORETIC IMAGING PROCESS EMPLOYING AN INSULATING CARRIER LIQUID CONTAINING AN UNSATURATED COMPOUND Raymond L. Jelfo, Sodus Point, N.Y., assignor to Xerox Corporation, Rochester, NY.

Filed May 29, 1967, Ser. No. 641,981

Int. Cl. G03g 5/00, 7/00, 17/00 U.S. Cl. 961 R 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to a monochromatic imaging system utilizing an imaging suspension comprising a photoresponsive pigment dispersed in an insulating carrier liquid. The insulating liquid carrier utilized in the process comprises a substantially non-volatile, unsaturated organic composition which is in liquid form at room temperature. The suspension is interpositioned between a pair of electrodes and subjected to a potential difference while simultaneously being selectively exposed to a light image. The monochromatic imaging process of the present invention produces relatively high contrast, background free images in a single pass system.

BACKGROUND OF THE INVENTION This invention relates to an imaging system, and more specifically, to a photoelectrophoretic imaging system.

In photoelectrophoretic imaging colored particles are suspended in an insulating carrier liquid. This suspension is then placed between a pair of electrodes, subjected to a potential difierence and exposed to an image to be reproduced. Ordinarily, in carrying out the process, the imaging suspension is placed on a transparent electrically conductive plate in the form of a thin film and exposure is made through the bottom of this plate while a second generally cylindrical shaped electrode is rolled over the top of the suspension. The particles are believed to bear an initial charge when suspended in the liquid which causes them to be attracted to the transparent base elec trode and to change polarity by exchanging charge with the base electrode upon exposure so that exposed particles migrate across to the roller electrode to form an image on the base electrode by particle subtraction. The system may be used to produce monochromatic images by using a single color particle in this suspension or a number of differently colored particles in this suspension which all respond to the same wavelength of light exposure. An extensive and detailed description of the photoelectrophoretic imaging technique as described above is found in copending U.S. patent applications Ser. Nos. 384,737; 384,681; and 384,680, filed Jan. 23, 1964, having a common assignee.

Although it has been found that good quality images can be produced, especially when a relatively insulating blocking electrode surface is used as one of the two electrodes in the system, with migration of the particles dependent upon the conditions of exposure, the unexposed photomigratory particles will also migrate in various degrees to either or both of the electrodes, thus demonstrating a dielectrophoretic property. The resulting contamination in the background areas leads to a degradation of the resulting images thereby producing low contrast reproductions in a monochromatic imaging system.

Therefore, it is an object of this invention to provide an imaging system which will overcome the above noted disadvantages.

It is a further object of this invention to provide a novel Patented Sept. 19, 1972 imaging system capable of producing high contrast, low background images.

Another object of this invention is to provide a high contrast single pass monochromatic imaging system capable of producing background free colored images.

It is still a further object of this invention to provide a novel electrophoretic monochromatic imaging system.

Yet, still a further object of this invention is to provide a novel monochromatic imaging composition.

SUMMARY OF THE INVENTION The foregoing objects and others are accomplished in accordance with this invention, generally speaking, by providing a suspension of photoresponsive imaging particles in an insulating carrier liquid. The insulating carrier liquid utilized in the process of the present invention comprises a substantially non-volatile, unsaturated organic composition which is liquid under ambient conditions. This suspension is interpositioned between a pair of electrodes and subjected to a potential difference while simultaneously being selectively exposed to a reproducible image. Generally speaking, the imaging suspension is placed on a transparent electrically conductive imaging plate or first electrode in the form of a thin film, and exposure is made through the transparent plate while in contact with a second electrode which is placed or rolled over the top of the imaging suspension. The pigment particles present in the suspension migrate in response to the electromagnetic actinic radiation to form a visible image pattern at one or both of the electrodes, the images being opposite in sense to one another. The resulting images produced in the single pass system are high contrast, substantially background free reproductions.

It has been determined in the course of the present invention that upon introducing a substantially non-volatile, unsaturated carrier liquid having a hydrocrabon nucleus into the photomigratory imaging suspension of the present invention the resulting images produced in a monochromatic imaging system are substantially free of background contamination thereby producing extremely high contrast reproductions. The carrier will generally be in liquid form under ambient or room conditions. Heretonow, materials similar in nature to those used in the present invention as the carrier liquid have been thought to be too conductive to satisfy the imaging requirements of the photoelectrophoretic imaging system herein utilized. It has now been demonstrated that the insulating carrier liquid proposed for use in the present imaging suspension is not only insulating enough to be compatible with the present process but in addition markedly enhances the image capabilities of the system.

DESCRIPTION OF THE DRAWING The invention is more specifically defined in the accompanying drawing in which there is seen a transparent electrode generally designated 1 which, in this instance, is made up of a layer of optically transparent glass 2 overcoated with a thin optically transparent layer 3 of tin 0X- ide. Tin oxide coated glass of this nature is commercially available under the tradename NESA glass from the Pittsburgh Plate Glass Co. This electrode shall hereafter be referred to as the imaging or injecting electrode. Coated on the surface of the injecting electrode 1 is a thin layer 4 of finely divided photosensitive pigment particles dispersed in an insulating carrier liquid. The term photosensitive, for the purposes of this application, refers to the properties of a particle which, once attracted to the injecting electrode, will migrate away from this electrode under the influence of an applied electric field when it is exposed to actinic electromagnetic radiation. A further detailed explanation of the apparent mechanism of the operation is disclosed in copending US. patent applica- 3 tions Ser. Nos. 384,681; 384,680; both filed July 23, 1964 and now abandoned and 384,737, now U.S. Pat. No. 3,384,565, having a common assignee, the disclosures of which are incorporated herein by reference.

The insulating carrier liquid utilized in the process of the present invention comprises a substantially non-volatile, unsaturated, natural occurring oil-like organic composition having a hydrocarbon nucleus which is a liquid at ambient conditions. Materials which have been found suitable for the present use include olive oil, castor oil, linseed oil, peanut oil, corn oil, and soybean oil. These compositions generally fall into a class of compounds known as glyceride esters of unsaturated fatty acids in which one or more of the hydroxyl groups of the glycerol constituent have been replaced by an acid radical. Other naturally occurring compounds which have been found useful include cotton seed oil and china wood oil (tung oil) derived from the seeds of plants; pine oil and cedarwood oil which are generally terpene compounds; and marine oils such as sperm oil and cod liver oil.

Above the liquid suspension is passed a second or blocking electrode 5, which, in this illustration, is represented as a roller having a conductive central core 11 connected to a power source 6. The core in this instance is covered with a layer of blocking electrode material 12 which may, for example, be polyurethane. A transfer sheet 13 of ordinary bond paper is attached to the outer surface of the roller. The blocking electrode is connected to one side of potential source 6 through a switch 7. The opposite side of potential source 6 is connected to the injecting electrode 1 so that when switch 7 is closed, an electric field is applied across the liquid suspension 4 between electrodes 1 and 5. The pigment suspension is exposed by way of the projector mechanism made up of a light source 8, a transparency 9, and a lens system 10. For purposes of this illustration a microfilm negative is used during the process. A potential is applied across the switch 7. A blocking electrode 5, having a cylindrical configuration in the present illustration, is rolled across the top surface of the injecting electrode 1 supporting the suspension 4 containing the photomigratory particles. Switch 7 is closed during the period of image exposure. The light exposure causes the pigment particles suspended in the carrier and originally attracted to the first electrode 1 to migrate in an imagewise manner through the liquid to the surface of the blocking electrode thereby producing a positive pigment image on the surface of the bond paper 13 While leaving behind a complementary image on the injecting electrode surface which is a duplicate of the original. It should be noted at this point of the discussion that although the blocking electrode in the present illustration is represented as a cylinder it may also take the form of a flat electrode, as in the case of the illustrated injecting electrode, in which instance it would be not necessary for the injecting electrode to be optically trasparent but instead the blocking electrode may be the optically transparent electrode and exposure made through it. The pigment image need not necessarily be formed on the paper substrate but may in fact be formed on the surface of the electrode. The pigment image may then be fixed in place, as, for example, by placing a lamination over its top surface such as by spraying with Kralon, a thermoplastic resin composition commercially available from the U.S. Rubber Corporation. The system herein described can produce high contrast monochromatic images with little or no background degradation.

As stated above, once the particle image is formed on one of the electrodes, or the paper transfer sheet, it may be fixed thereon as by spraying a binder on it or by laminating an overlay over it. If imaged on the electrode surface, it will be found preferable to transfer the image from the electrode and fix it on another surface so that the electrode may be reused. Such a transfer step may be carried out by adhesive pickofl with an adhesive tape,

such as Scotch brand cellophane tape or preferably by electrostatic field transfer. Electrostatic transfer may, for example, be carried out by carryin out the imaging procedure described above and then passing a second roller over the particle image formed on the desired imaged electrode, the second roller being held at a potential opposite in polarity to that of the imaged electrode. If the first electrode roller is covered with a transfer paper sleeve, as in this illustration, or the blocking material consists of a baryta paper sleeve, more fully described below, this paper sleeve will pick up the complete image on the initial pass. All that is then required is to remove the sleeve bearing the image and replace it with a like material.

When used in the course of the present invention, the term injecting or imaging electrode should be understood to mean that it is an electrode which will preferably be capable of exchanging charge with the photosensitive particles of the imaging dispersion when the dispersion is exposed to light so as to allow for a net change in the charge polarity on the particle. By the term blocking electrode is meant one which is capable of injecting electrons into or receiving electrons from the above mentioned photosensitive particles at a negligible rate when the particles come into contact with the surface of the electrode. Obviously if all polarities in the system are reversed, the function of the electrodes will also be reversed.

It is preferred that the injecting electrode be composed of an optically transparent material, such as glass, overcoated with conductive materials such as tin oxide, copper, copper iodine, gold, or the like to obtain optimum results; however, other suitable materials including many semiconductive materials such as raw cellophane which are ordinarily not thought of as conductors but which are still capable of accepting injected charge carriers of the proper polarity under the influence of the applied field, may 'be used within the course of the present invention. The use of more conductive materials allows for clearer charge separation and the charge leaving the particles upon exposure can move into the underlying surface and away from the particle on which it originated. This also prevents possible charge buildup on the electrode which tends to diminish the interior electrode field. The blocking electrode, on the other hand, is selected so as to prevent or greatly retard the injection of electrons into the photosensitive pigment particles when the particles reach the surface of this electrode. The blocking electrode drum or plate generally will consist of a material which is fairly high in electrical conductivity. Typical conductor materials are conductive rubber and metal foils of steel, aluminum, copper and brass. Preferably, the core of the drum or base of the plate will have a high electrical conductivity in order to establish the required polarity differential. However, if a low conductivity material is used a separate electrical connection may be made to the back of the blocking layer of the electrode. Although a blocking electrode material need not necessarily be used in the system, the use of such a layer is preferred because of the markedly improved results which it is capable of producing. It is preferred that the blocking layer, when used, be either an insulator or a semiconductor which will not allow for the passage of sufiicient charge carriers under the influence of the applied field to discharge the particles finely bound to it, thereby preventing particle oscillation in the system. The result is enhanced image density and resolution. Even if this blocking electrode will allow for the passage of some charge carriers through it to the photosensitive particles, it will still be considered to come within the class of preferred materials if it does not allow for the passage of sulficient carrier to recharge the particles to the opposite polarity. Exemplary of the preferred blocking materials used are baryta paper, which consists of paper coated with barium sulfate suspended in a gelatin solution, Tedlar, a polyvinyl fluoride commercially available from E. I. du Pont de Nemours and polyurethane coatings. Any other suitable material having a resistivity of about ohms per sq. cm. or greater may be employed as the blocking electrode material. Typical materials in this resistivity range include cellulose acetate coated papers, cellophane, polystyrene, polytetrafiuoroethylene, and polyethylene terephthalate. The baryta paper, Tedlar, and the other suitable materials used as the blocking layer may be wetted on their back surface with tap water or coated on the back surface with electrically conductive materials. The blocking electrode layer, when utilized, may be a separate replaceable layer which is either taped to the blocking electrode or held by mechanical fasteners or any other device which is capable of releasably holding the layer on the electrode. In the alternative, the layer may be an integral part of the electrode itself, being either adhesively bound, laminated, spray coated or otherwise applied to the surface of the roller. Other materials that may be used in the injecting and blocking electrodes, other photosensitive particles which may be used as the photomigratory pigments and the operating conditions utilized with the system are to be found in the above mentioned copending U.S. patent applications Ser. Nos. 384,737; 384,680; and 384,681, having a common assignee.

Any suitable voltage may be applied, depending upon the thickness of the materials used, to produce a preferred field strength of from about 400 to about 1000 volts per mil across the suspension at the time of exposure. For example, using a 7 mil thick plastic coated baryta paper over a conductive neoprene (polychloroprene) support as the blocking electrode, when this electrode contacts the injecting electrode in the presence of the imaging suspension it has generally been found that from about 1000 to about 7000 volts may be employed and that ordinarily better images are produced it the applied voltage is at the higher end of this range. Different voltages may be used with difierent components of varying thickness to attain approximately the same field strength in the system.

As set out above, any suitable insulating, substantially non-volatile, unsaturated vehicle which is liquid at room temperature and has a hydrocarbon nucleus may be used as the carrier in the present invention. Typical such generally naturally occurring compositions include: olive oil, cotton seed oil, china wood oil, linseed oil, castor oil, pine oil, cedarwood oil, peanut oil, corn oil, soybean oil, and various marine oils such as cod liver oil, sperm oil and mixtures thereof. These carrier liquids may be used either alone or in conjunction with saturated aliphatic hydrocarbon carrier liquids such as decane, dodecane, ntetradecane, and Sohio Odorless Solvent, a kerosene fraction commercially available from the Standard Oil Co. of Ohio. The carrier liquid of the present invention will contain at least about 10% of the substantially nonvolatile unsaturated liquid component when blended with .other more conventional carrier materials such as the aliphatic hydrocarbons described. In order to obtain optimum results, the unsaturated component is present in the carrier liquid in a preferred range of from about 10 to about 100% of the vehicle employed.

It is to be understood that any suitable photomigratory material may be employed in the course of the present invention with the choice depending largely upon the photosensitivity and the spectral sensitivity required, and the degree of contrast desired the final image. Typical photoresponsive materials include: substituted and nonsubstituted phthalocyanine, quinacridones, zinc oxide, Algol Yellow [1,2,S,6-di(C,C'-diphenyl)diazo-anthraquinone] (C.-I. No. 67300), cadmium sulfide, cadmium selenide, iron oxide (F6203), selenium, antimony sulfide, arsenic sulfide, 3-benzylidene aminocarbazole, 3-amino carbazole, Watchung Red B [1-(4-methyl-5'-chloroazobenzene-2'-sulfonic acid)-2-hydroxy 3-napthoic acid] (Cl. No. 15865), and mixtures thereof. The liquid imaging suspension may contain one or more different photosensitive particles having different ranges of spectral response. In the monochromatic system of the present invention, the particles included in the imaging suspension may be virtually any color in which it is desired to produce the final image, such as gray, black, blue, red, green, etc. and a particular range of its spectral response is relatively immaterial.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To further define the specifics of the present invention, the following examples are intended to illustrate and not limit the particulars of the present system. Parts and percentages are by weight unless otherwise indicated.

In the following examples, the imaging or injecting first electrode is made up of NESA glass, as described above. The development or blocking electrode consists of a conductive steel core coated with a layer of polyurethane, unless otherwise indicated. A transfer paper sleeve is attached to the development electrode. A potential differ ence of about 7000 volts is applied across the imaging suspension.

EXAMPLE "I A commercial, metal-free phthalocyanine is purified by acetone extraction to remove organic impurities. Since this extraction step yields the less sensitive beta crystalline form, the desired alpha form is obtained by dissolving grams of the beta form in 600 cc. of sulfuric acid, precipitating it by pouring the solution into 3000 cc. of ice water and washing with water to neutrality. The thus purified alpha phthalocyanine is then salt milled for 6 days and desalted by slurrying in distilled water, vacuum fi1tering, water washing, and finally methanol washing until the initial filtrate is clear, thus, producing x-form phthalocyanine. After vacuum drying to remove residual methanol, the x-form phthalocyanine produced is used to prepare an imaging suspension according to the following formulation:

Phthalocyanine (x-form) grams 2.5 Tricresyl phosphate do .05 Trinitrofluoronone do .05 Sperm oil (ADM 38.0 BW) cc 60 The phthalocyanine is ground in a mortar, placed in a Waring Blendor with the other ingredients and dispersed for about 10 minutes at high speed. The resulting suspen sion is coated on the surface of a NESA glass electrode. As the blocking electrode with paper sleeve is passed across the surface of the suspension liquid, at a rate of about 5 in./sec., the potential difference stated above is established and the suspension selectively exposed to a light intensity of about 50 foot-candles through a transparent negative with a General Electric visible light source. By a single material transfer a high quality positive image is formed with little or no background (less than .01 density units) on the surface of the paper sleeve.

'EXAMPIJE II The process of Example I is repeated with the substitution of the following imaging formulation:

Phthalocyanine (x-form) grams 2.6 Tricresyl phosphate do 0.5 Sperm oil (ADM 38.0 BW) cc 60 Results similar to those obtained in Example I are achieved.

EXAMPLE 111 The process of Example I is repeated with the substitution of the following imaging formulation:

Phthalocyanine (x-form) grams 4 Algol Yellow do 1 Tricresyl phosphate do 1 Trinitrofluoronone do 0.2 4,4 dibromobiphenyl do 0.2 Sohio Solvent 3454 cc 70 Sperm oil (ADM 38.0 BW) cc 28 High contrast, low background positive images are produced on the paper sleeve.

EXAMPLE IV The process of Example I is repeated using the same formulation with the exception that linseed oil is substituted for the sperm oil. Similar results are obtained.

EXAMPLE V The process of Example I is repeated utilizing the same formulation with the exception of substituting corn oil for the sperm oil carrier liquid. A high quality, low background positive image is produced on the paper sleeve of the blocking electrode.

EXAMPLE VI The process of Example II is repeated with the exception of the substitution of soybean oil for the sperm 011 of the imaging formulation. Similar results are obtained.

EXAMPLE VII The process of Example III is repeated utilizing the same formulation with the exception of the substitut on of peanut oil for the sperm oil of the particular imaging suspension. High quality images are obtained.

EXAMPLE VIII The process of Example III is repeated with the exception of the substitution of china wood oil for sperm oil in the imaging formulation. High contrast images are obtained.

EXAMPLE IX An imaging suspension is formulated for use in the process of the present invention excluding the use of the trast image with high background. The result of this example demonstrates the eiiect that the unsaturated additive of the present invention has on the resulting images produced.

EXAMPLE X The process of Example I is repeated with the exception that the Sohio 3454 solvent is substituted for the sperm oil additive. The resulting poor images produced further illustrate and demonstrate the advantageous effect obtained with the use of the unsaturated carrier liquid component of the present invention. The resulting images in this example were of a low contrast quality with high background density.

Although the present examples were specific in terms of conditions and materials used, any of the above listed typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used to carry out the process of the present invention, other steps or modifications may be used, if desirable. For example, the process may be readily adapted to be used in a continuous imaging system. In addition, other materials may be incorporated in the imaging suspension, injecting electrode, or blocking electrode to enhance, synergize, or otherwise desirably eifect the properties of this system for their present use. For example, the imaging suspension may contain sensitizers for the photoconductive particles which are dissolved or suspended in the carrier liquid.

Anyone skilled in the art will have other modifications occur to him based on the teachings of the present invention. These modifications are intended to be encompassed within the scope of this invention.

What is claimed is:

1. A method of forming a monochromatic image comprising interpositioning an imaging suspension between a first and second electrode said first electrode being transparent to electromagnetic radiation, said imaging suspension comprising a photoresponsive pigment dispersed in an insulating carrier liquid said carrier liquid comprising at least about 10% by weight of a substantially non-volatile, unsaturated, natural occurring oil-like compound having a hydrocarbon nucleus, and which is liquid under ambient conditions, applying an electric field to said imaging suspension between said electrodes, simultaneously exposing said suspension to an image through said transparent electrode with a source of activating electromagnetic radiation to form a pigment image on at least one of said electrodes.

References Cited UNITED STATES PATENTS 3,384,565 5/1968 Tulagin et al. 961.2

3,401,037 9/1968 Roteman et al 961 FOREIGN PATENTS 1,203,606 10/1965 Germany 96-1 U.S. Cl. X.R. 96-l.5; 204-181 

